1. Field of the Invention
This invention relates to pattern making devices for objects of geometric cross-section and more particularly pattern making devices of the type that can trace all variations of contour an object may have within a given plane.
2. Description of the Prior Art
The pattern making device of the present invention, and the method of using same, are particularly well suited for use in the construction industry, particularly in the construction of concrete buildings or parking garages utilizing poured concrete columns. Once a concrete column has been poured, a concrete floor is poured around the top of it. A form that patterns the concrete column must be placed around the column so that when the concrete floor is poured, seepage of concrete around the column and onto the area below is minimized.
Concrete columns poured during construction of these buildings and parking ramps are of a specified size. However, custom cutting of a pattern in the plywood that will ultimately fit around the column is required because of the manner in which the concrete hardens or sets. Variations in the moisture content of the concrete mix and the loading due to the weight of the column cause bulges and variations around the circumference of the column in any given plane.
Current construction methods are based on trial and error. First, a circle of near the optimum diameter of the column is cut from a piece of plywood. One man then sets the polywood over the column and another traces the areas that need to be cut away, observing and marking from underneath the plywood. Once the second man has traced a pattern on the underneath surface of the plywood, the plywood is removed from over the column and a second cut is made. This process is repeated until the hole that is cut is patterned to fit the surface of the concrete column.
The pattern cut out from the plywood by using the above method is seldom exact. Concrete can seep between the column and the plywood. Certain jobs make concrete seepage around the columns contrary to the specification.
Additional obvious drawbacks to the present method of making these patterns is the time involved in doing so. At least two cuts are required and at least two men are required.
Pattern making devices utilizing sliding pins to describe a contoured surface are commercially available. These devices are longitudinal structures only, having no provision for circumscribing the plane of an object of a geometric transverse cross-section. The longitudinal devices are currently used by woodworkers and furniture makers. A precise pattern of a curvilinear surface can be retained by the device and transferred to the surface of another piece of wood. Tracing the retained contour onto the surface of a piece of wood and cutting along the line traced results in a pattern that can be used to cut an identical curvilinear piece of wood.
Adaption of a pattern making device of the type previously known in longitudinal form only to the pouring of concrete columns is impractical. Several distinct patterns would have to be retained, the wooden surface from which the pattern would be cut would have to be very precisely marked and a tracing of a portion of the object transferred to the wooden surface from the pattern making device. The process would have to be repeated until the entire perimeter of the geometric object was circumnavigated.
To attempt to do this is not only time consuming but in all probability cannot accurately be done by a carpenter on the job. The prior art devices are therefore unacceptable when the perimeter of a circular or a square cross sectional object is to be patterned.